NASA AND ITS US industry team members are preparing to make major airframe and propulsion-system selections in December as the High Speed Research (HSR) programme moves into Phase II.
The HSR project is designed to provide a technology base by 2001, which will support a US industry decision on whether to go ahead with a second-generation supersonic transport. US industry, led by air-framers Boeing and McDonnell Douglas (MDC), and by engine makers General Electric and Pratt & Whitney, is heavily involved in the HSR programme as well as its independent High Speed Commercial Transport (HSCT) studies.
Data from these mainly market-driven studies will also be a factor in the decision, which could lead to production beginning in 2006.
GE and P&W, leading the HSR propulsion studies, are preparing to conduct major tests of a mixed-flow turbofan fitted with a mixer ejector during the third and fourth quarters of this year. The results will help the team in the selection of major propulsion concepts to pursue from 1996 onwards.
The tests will attempt to quantify the amount of thrust loss associated with a mixer ejector as it forces ambient air to mix with the core exhaust during take-off. This combination was selected by GE and P&W as the best way to meet Stage 3 noise rules after joint studies of a large number of engines.
The interactions of the large inlet, designed by Boeing and MDC, and the Allison-developed exhaust nozzle will also be tested using computational fluid dynamics and other techniques.
Tests to date suggest that the final length of the power plant will be more than 15m (50ft). Of this, 6.7m will be made up by the inlet, 3.6m by the gas generator and 5.2m by the nozzle. At the design speed of Mach 2.4, more than half of the pressure rise will be created in the inlet while, at the same cruise speed, there will be six times the amount of expansion in the exhaust nozzle as in the turbine section.
Studies will also be made of the inlet design and a choice is expected between a two-dimensional and an axisymmetric design.
A mixed compression inlet is "definitely needed" and studies will be made of the "unstart" recovery and its potential impact on the engine design. The phenomenon is well known in the Lockheed SR-71, which suffers occasional "unstarts" when flow distortion into the inlet sometimes causes an engine surge, leading to a flame-out.
The Aerospatiale/British Aerospace Concorde does not suffer from "unstarts" because the intake air is compressed externally.
Source: Flight International
